Advances in integrated circuit manufacturing technologies make possible electronic systems comprising tens or even hundreds of millions of active devices. In addition, increased numbers of interconnection layers provide for more signal wiring and more complex control schemes. Among other things, the demand for such systems has led to increased system performance, decreased device size, and greater feature sets. The direct result of system and technology improvements is ever increasing design complexity. The design complexity drives engineering challenges with regard to circuit design, system implementation and control, chip fabrication, and the like. This complexity has for example, driven greater scrutiny of the logic circuits, interconnection schemes, systems architectures, and controls. As a result, new technologies, architectures, and circuit families have been developed which can take advantage of reduced total device count, smaller device sizes, and simplified wiring/control schemes. These circuit families each provide certain benefits and costs, each requiring its own careful design considerations.
Logic circuits fall into two broad categories, static circuits and dynamic circuits. Static circuits find many applications where signal integrity and system robustness are paramount design criteria. In contrast, dynamic circuits find many applications where system performance and circuit density are paramount. Personal computer memories and microprocessors are typical examples of circuits that demand high circuit density with high system performance. Interest has been focused on circuit families that can drastically reduce the amount of clock and control signal interconnect required to support them. For example, circuit families that do not require a clock signal, such as asynchronous or self-timed circuits, have distinct advantages over their clocked counterparts because the need for external control signals is reduced or eliminated. Further, circuit families that can provide for the local generation of required control signals may further reduce wiring and control complexity.